Technology & Engineering
Open Channel Flow
Open channel flow refers to the movement of fluid in a conduit with a free surface, such as rivers, canals, and streams. It is characterized by the presence of air above the fluid and is governed by principles of fluid mechanics and hydraulics. Engineers and scientists study open channel flow to understand and manage water resources, design hydraulic structures, and mitigate flood risks.
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9 Key excerpts on "Open Channel Flow"
- Andrew L. Gerhart, John I. Hochstein, Philip M. Gerhart(Authors)
- 2023(Publication Date)
- Wiley(Publisher)
535 535 = CHAPTER 10 Open-channel flow involves the flow of a liquid in a channel or conduit that is not completely filled. A free surface exists between the flowing fluid (usually water) and fluid above it (usually the atmosphere). The main driving force for such flows is the fluid weight—gravity forces the fluid to flow downhill. Most open-channel flow results are based on correlations obtained from model and full-scale experiments. Additional information can be gained from analytical and numerical efforts. Open-channel flows are essential to the world as we know it. The natural drainage of water through the numerous creek and river systems is an example of open-channel flow. Although the flow geometry for these systems is extremely complex, the resulting flow prop- erties are of considerable economic, ecological, and recreational importance. Other examples of open-channel flows include the flow of rainwater in the gutters of our houses; the flow in canals, drainage ditches, sewers, and gutters along roads; the flow of small rivulets and sheets of water on a road during a rain; and the flow in the chutes of water rides in amusement parks. Open-channel flow involves a free surface that can deform. Therefore, a brief introduc- tion to the properties and characteristics of surface waves is included. The purpose of this chapter is to investigate the basic features of open-channel flow. Because of the amount and variety of material available, only a brief introduction to the topic can be presented. Further information can be obtained from the references indicated. 10.1 GENERAL CHARACTERISTICS OF OPEN-CHANNEL FLOW In our study of pipe flow (Chapter 8), we found that there are many ways to classify a flow— developing, fully developed, laminar, turbulent, and so on. For open-channel flow, the existence of a free surface allows additional types of flow.
eBook - PDF- D.J. Stephenson(Author)
- 1981(Publication Date)
- Elsevier Science(Publisher)
198 CHAPTER 12 OPEN CHANNELS STORMWATER CHANNELS Open stormwater channels provide an economical and sometimes essential alternative to closed drains. It is a fact that open channels o r f e r less frictional resistance due to the smaller wetted perimeter, and consequently require smaller cross sections, than closed conduits. The factor of safety against flooding of a channel is generally greater than that of a pipeline. A small water level rise in a channel increases the discharge capacity disproportionately (discharge is nearl) proportional to €low depth to the power of 5 / 3 ) whereas in the case of a pipe, the discharge capacity is only proportional to the square root of thc hcad. Thus rapid overflowing of mar.holes associated with closed drains and excess surface flow will result with storms more severe than the design storm. An open channel can be an obstruction or hazard, especially if wide or deep. Open channels may also require regular maintenance due to deposits or vegetation growth. On the other hand, grassed and contoured channels can bc attractive. Shallow channels can form natural barriers between traffic and pedestrians without being dangerous. Above a l l , channels are more economical than closed drains. Where land is not too valuable and space is allowed at planning stage, channels may be the solution. Away from built up areas, natural water- courses arc generally employed, although protective works may be necessary to avoid erosion. FI.OW CLASSIFICATlON The depth oi flow in a channel will depend on the flow rate, slope, cross sectional shape and boundary roughness. Even then the water depth and velocity can change in time and space. This may be due to variation in flow rate, non-equilibrium or variations in channel alignment and cross section. Thus the assumption of steady, uniform flow consistent with the discharge rate is often incorrect and depth requirements may be greater than indicated by uniform flow theory.
eBook - ePub- Myer Kutz(Author)
- 2018(Publication Date)
- Wiley(Publisher)
2013 ) has 81 chapters and over 1100 pages in 2 volumes), this chapter can only provide a brief overview of the dominant processes that control heat, mass, and pollutant transport in the environment. The material presented in this chapter is quite theoretical and, at times, abstract, with the goal of providing the mathematical underpinnings of some of the models presented in the more applied chapters. The chapter assumes a solid knowledge at the undergraduate level of fluid mechanics and calculus including fluid properties, control volume analysis of mass, energy, and momentum, scalar conservation laws, dimensional analysis, open‐channel flow, and ordinary and partial differential equations. All sections in this chapter include extensive reference lists for further reading.The first three sections below review free surface and subsurface flows. In Section 10.1 Dr. Abdul Khan reviews the modeling of open‐channel flow including reviews of steady uniform flow, sub‐ and supercritical flow, flow control, and gradually varied flow (GVF). Surface waves are described by Dr. Firat Y. Testik in Section 10.2 , while in Section 10.3 Dr. Khan reviews the mechanics of flow in porous media and its application to infiltration and groundwater flow. Dr. Nigel B. Kaye covers the basics of pollutant transport through advection and diffusion in Section 10.4 . This section presents the basic advection diffusion equations and the solution to a set of idealized problems that illustrate basic behavior. The chapter concludes with detailed discussions of turbulent shear flows including turbulent jets (Section 10.5 , Dr. Khan), turbulent plumes (Section 10.6 , Dr. Kaye), and gravity currents (Section 10.7 , Dr. Testik).10.1 Open‐Channel Flow
Open‐channel flow is a gravity‐driven flow with a free surface that is exposed to atmospheric pressure. Open‐channel flow can occur in rivers, canals, culverts, and sanitary sewers. Open‐channel flow can be identified as steady flow, unsteady flow, uniform flow, and nonuniform flow. The flow in an open channel is unsteady if the flow properties such as depth, velocity, and/or discharge are changing with time at a specific channel cross section. In some instances an unsteady flow can be transformed into a steady flow by coordinate transformation, i.e., having a coordinate system that is based on a moving frame of reference. A more general definition can be construed by realizing that for steady flow the local acceleration is zero. Uniform and nonuniform flows are determined based on the variation of flow properties along the length of the channel or along the flow direction at a given instance in time. The variations of velocity within a channel cross section are ignored. If the flow properties do not change along the channel length or the convective acceleration is zero, the flow is deemed uniform (Henderson, 1966 ; Chin, 2006 ; Chaudhry, 2008
eBook - PDF- John Ward-Smith(Author)
- 2018(Publication Date)
- CRC Press(Publisher)
10 Flow with a free surface 10.1 INTRODUCTION In previous chapters, a flowing fluid has usually been assumed to be bounded on all sides by solid surfaces. For liquids, however, flow may take place when the uppermost boundary is the free surface of the liquid itself. The cross-section of the flow is not then determined entirely by the solid boundaries, but is free to change. As a result, the conditions controlling the flow are different from those governing flow that is entirely enclosed. Indeed, the flow of a liquid with a free surface is, in general, much more complicated than flow in pipes and other closed conduits. If the liquid is bounded by side walls – such as the banks of a river or canal – the flow is said to take place in an open channel . The free surface is subjected (usually) only to atmospheric pressure and, since this pressure is constant, the flow is caused by the weight of the fluid – or, more precisely, a component of the weight. As in pipes, uniform flow is accompanied by a drop in piezometric pressure, p + % gz , but for an open channel it is only the second term, % gz , that is significant, and uniform flow in an open channel is always accompanied by a fall in the level of the surface. Open channels are frequently encountered. Natural streams and rivers, artificial canals, irrigation ditches and flumes are obvious examples; but pipe-lines or tunnels that are not completely full of liquid also have the essential features of open channels. Water is the liquid usually involved, and practically all the experimental data for open channels relate to water at ordinary temperatures. Even when the flow is assumed to be steady and uniform, complete solu-tions of problems of open-channel flow are usually more difficult to obtain than those for flow in pipes. For one thing there is a much wider range of con-ditions than for pipes.
eBook - ePubOpen Channel Hydraulics, River Hydraulic Structures and Fluvial Geomorphology
For Engineers, Geomorphologists and Physical Geographers
- Artur Radecki-Pawlik, Stefano Pagliara, Jan Hradecky, Artur Radecki-Pawlik, Stefano Pagliara, Jan Hradecky(Authors)
- 2017(Publication Date)
- CRC Press(Publisher)
Chapter 1Principles of Hydraulics of Open Channels
Stefano Pagliara and Michele PalermoDESTEC – Department of Energy, Engineering, Systems, Land and Construction, University of Pisa, Via Gabba 22, 56122, Pisa, Italy.E-mail: [email protected] * Corresponding author: [email protected]Introduction
Open Channel Flow can be classified according to the characteristics of the channel. Namely, Open Channel Flow can occur both in natural streams and rivers and in artificial channels, such as drainage channel systems, sewer pipes, concrete/earth channels, etc. According to the geometry of the channel, the water discharge can flow either in prismatic channels (generally characterized by a constant transversal cross‐section geometry and longitudinal slope) or in non‐prismatic channels (natural streams or rivers, in which both the transversal cross‐section geometry and longitudinal bed slope vary). Furthermore, channel bed characteristics also contribute to distinguish the Open Channel Flows, due to the roughness conditions and erosive process, which can contribute to the modification of the channel geometry. In other words, the channel bed can be smooth, rough, erodible, fixed, etc. Therefore, the flow characteristics modify accordingly. In general, two main distinctions can be done according to the flow characteristics variation with time and along the channel (Chow 1959; Citrini and Noseda 1987; De Marchi 1986; Henderson 1966). Considering the flow characteristics along the channel, uniform flow conditions (UF) occur when the discharge Q , the water depth y and the average flow velocity u at every cross‐section do not vary. Namely, at the generic cross‐ section (located at the longitudinal distance x respect to a selected reference system), the following conditions should be verified:(1)=∂ y∂ x=∂ Q∂ x= 0∂ u∂ xThese analytical conditions occur only when the cross‐section geometry do not vary. Therefore, if the water depth is constant, from (Eq. 1 ) it can be easily deduced that the free surface should be parallel to the channel bed (see Fig. 1
eBook - PDFSediment Transport in Irrigation Canals
A New Approach
- Herman Depeweg(Author)
- 2014(Publication Date)
- CRC Press(Publisher)
This chapter will introduce some main aspects of open channel hydraulics in order to be used as tools in the following chapters, which will deal with the movement of sediments and water together. In some cases the water flow varies over time and becomes unsteady. For some 10 Sediment Transport in Irrigation Canals applications the variation may be considered to be so slow that a steady (or quasi steady) flow can be assumed. Considering the spatial distribution, any flow is essentially three-dimensional, meaning that the magnitude and direction of the flow vary from one point to another. Knowledge of this three-dimensional flow behaviour is still limited; but in many engineer-ing applications it is often sufficient to know particular mean or average values. The mean value can be presented for: • a two-dimensional flow situation by averaging the value over the canal depth at a certain point; an example is the depth-averaged flow velocity in a vertical; • a two-dimensional flow condition by averaging the value over the canal width (in a lateral direction); an example is the average water depth in a cross-section; • a one-dimensional flow situation by averaging the value over the whole cross-section. The resulting values depend on the longitudinal coordinate (the x -values); an example is the average velocity in a cross-section. It is important to remember that most of the two-and one-dimensional flow problems are simplified by averaging the flow characteristics; some information relating to the ‘un-averaged’ three-dimensional situation and the consequences of the process of averaging should be considered when the mean quantities are interpreted. Open Channel Flow can be classified in many ways. A very common classification of open channel (gravity) flow is according to the change of flow depth with respect to time and space and is shown in Figure 2.1.
eBook - PDF- Hormoz Pazwash(Author)
- 2016(Publication Date)
- CRC Press(Publisher)
25 2 Pipe and Open Channel Flow A Review Hydraulic principles including energy equations, specific energy, and critical flow are briefly dis-cussed in this chapter. Also presented in this chapter is flow in pipes and open channels. This chap-ter also discusses losses in manholes and junctions. 2.1 FLOW CLASSIFICATIONS Since the design equations for pipes and channels have been developed for specific flow conditions, it is first necessary to classify the types of flow. Depending on temporal and spatial variations, the flow may be classified as steady or unsteady, uniform or nonuniform, gradually varied or rapidly varied. In the design of pipes and channels in urban storm water management systems, the flow is generally considered steady and uniform, in that the flow velocity, discharge, and depth are assumed to remain unchanged with time or distance along a reach of a conduit. The depth of uniform flow is called the “normal” depth. Uniform flow can occur as pressure flow, such as full flow in pipes, or nonpressure (also called free surface flow), such as flow in channels and pipes when partially full. Nonuniform flow is a flow with changing depth and velocity along the channel or conduit. This type of flow can be gradually varied, if the changes in depth and velocity are gradual and occur over a considerable length, or rap-idly varied flow where the changes in flow are abrupt and occur over a very short distance. Overland flow on paved surfaces, gutter flow along roadways, and flow in natural streams are examples of gradually varied flow. Flow over emergency spillways, hydraulic jumps, and flow under sluice gates are examples of rapidly varied flow. The uniform flow equations can be (and commonly are) applied to short distance intervals in gradually varied flows; however, these equations are not applicable to rapidly varied flows. 2.2 ENERGY EQUATION A flowing fluid has potential, pressure, and kinetic energies at any given point.
eBook - ePubA New Approach to Sediment Transport in the Design and Operation of Irrigation Canals
UNESCO-IHE Lecture Note Series
- Herman Depeweg, Néstor Méndez V(Authors)
- 2007(Publication Date)
- CRC Press(Publisher)
CHAPTER 2Open Channel Flow2.1 INTRODUCTION
Irrigation canals form a complicated hydraulic system as they have to handle the motion of water and sediment as well as the mutual interaction of both motions. Flowing water transports sediment, this sediment causes changes in the bed and on the sides of the canal, which also influences the water movement. Hence, sediment transport and water flow are interrelated and cannot be separated; they influence each other in an implicit manner. The time scales of the two processes in canals are different (see Chapter 4 ) and therefore, the water flow and sediment transport can, in the first instance, be treated separately to specify their specific properties and characteristics.However, to predict the topological changes in a canal the two phenomena also have to be considered in conjunction. The objective of these lecture notes is to present a description of the sediment transport concepts in irrigation canals and, therefore, only those hydraulic aspects that are necessary for a better understanding of the sediment transport will be discussed. This chapter will present a short overview of the main hydraulic principles in Open Channel Flow, a short description of the dimensionless numbers used in the sediment concepts and a classification of flow types. In addition, a summary of the uniform and non-uniform theories for steady and unsteady flows is included. For more information on the hydraulic theories, reference will be made to handbooks and lecture notes on hydraulics.2.2 FLOW TYPES AND CHARACTERISTICS
Phenomena in open channels that convey water may vary considerably in magnitude and also sometimes in direction, both in terms of time and space. This chapter will introduce some main aspects of open channel hydraulics in order to be used as tools in the following chapters, which will deal with the movement of sediments and water together. In some cases the water flow in canals varies over time and becomes unsteady. For some applications the variation may be considered to be so slow that a steady (or quasi steady) flow can be assumed. Considering the spatial distribution, any flow is essentially three-dimensional, meaning that the magnitude and direction of the flow vary from one point to another. Knowledge of this three-dimensional flow behaviour is still limited; but in many engineering applications it is often sufficient to know particular mean or average values.
eBook - PDF- Xixi Wang(Author)
- 2021(Publication Date)
- Cambridge University Press(Publisher)
6 Open Channel Flow and Channel Design 6.1 Hydraulic and Energy Grade Lines 239 6.2 Normal Depth and Critical Depth 242 6.3 Gradually Varied Flow 245 6.4 Rapidly Varied Flow 257 6.5 Flow Measurement 270 6.6 Channel Design and Analysis 279 Problems 302 Open Channel Flow, which has a free water surface subject to atmosphere pressure, occurs in both natural and manmade channels. Its analysis is imperative to the design and management of water resources engineering projects such as levees and channels. This chapter discusses water surface profile classification and computation, flow measuring, and channel design. First, it discusses the principles of hydraulic and energy grade lines, normal depth, and critical depth. Second, it dis- cusses the water surface profile of gradually varied flow. Third, it discusses the water surface profile and energy loss of rapidly varied flow. Herein, along a homogenous channel segment, which has a fixed cross section, a constant roughness, and an invariant bed slope, gradually varied flow has a linear water surface, whereas rapidly varied flow has a curved water surface. Fourth, the chapter discusses weirs, flumes, and ultrasonic flow meters used for flow measurement. Finally, it discusses the methods of designing non-erosive, erosive, and semi-erosive channels. 6.1 Hydraulic and Energy Grade Lines At a given location of an open channel, as discussed in Sections 2.3 and 2.4.2, the water surface elevation, which represents the hydraulic energy head, is equal to the summation of the channel bed elevation and the water depth, and the total energy head is equal to the summation of the hydraulic energy head and the velocity head. As illustrated in Figure 6.1, the hydraulic grade line (HGL) defines how the water surface elevation varies along the flow direction in the channel and the energy grade line (EGL) defines how total energy head varies along the flow direction in the channel.
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